1. Technical Field
The present invention is generally related to multimedia delivery over the Internet. Particularly, the present invention is related to techniques of securing pieces of data or data segments that are distributed in client machines.
2. Description of the Related Art
U.S. application Ser. No. 11/076,334 describes a distributed architecture in which data for a multimedia title (e.g., a movie) is fragmented into a plurality of segments that are then distributed into client machines in services. Despite a unique way to fragment the data for a title, each of these segments is distributed to one or more of the client machines. When an order is received from an ordering machine that locally caches none or at least one but not all of the segments for the title, a set of other client machines are designated to supply the missing segments to the ordering machine. While playing back the title, the missing segments are concurrently streamed in and reassembled in the ordering machine to continue the playback of the title.
When there are a large number of subscribers, there must be many client machines in service. It is noticed that more than one client machine may have an identical copy of a segment of a title, and, as a result, there are more than one distributed copies of the title collectively in all the client machines. Although the data for the title or each segment is encrypted, if a malicious user somehow obtains a corresponding decryption key(s), he may compromise the encryption of all segments of the title from a group of client machines. Consequently, data for other titles offered in a library is subject to a possible attack from the malicious user (i.e., attacker).
One way for an attacker to obtain a decryption key(s) or initiate an abusive process may be briefly summarized as follows:                The attacker orders a title from his authenticated box that initiates a request to a server.        The server ensures that the missing segments for the title are downloaded to the attacker's box.        The server provides the decryption key(s) to the attacker's box in a form such that only a trusted agent (e.g., smart card, secure microprocessor, secure software) on that box is able to read the keys.        The attacker breaks this trusted agent and obtains the keys.        
Once obtaining the keys in this fashion (or some other way), the attacker could use them in many different ways. For example, the attacker may distribute the keys to others. With the keys, anyone can reassemble the encrypted data for a title by accessing a few client machines and reading the encrypted segments off the storage therein to recover all data for the title, and possible other titles.
U.S. application Ser. No. 11/076,334 presents one exemplary case in which distributed data may be subject to attacks. There are many other cases, especially in a distributed computing environment, that may present similar vulnerability. Thus, there is a need for techniques to prevent a malicious user from compromising other segments corresponding to a title even if the malicious user has already obtained a decryption key(s).